Common Causes
1) Net catch injury: the #1 cause. Always use a large container instead of net. 2) Jumping into hood: crack-line scales tear off. 3) Tank mate territorial fight.
Sudden scale loss without injury = likely ulcer disease (bacterial) — requires treatment.
First Aid
Do a 50% water change immediately. Add 1 tsp aquarium salt per 10L (0.1% salinity) for 5-7 days.
Dose melafix or pimafix at label rate for 7 days. Monitor for secondary fungal or bacterial infection.
Regrowth Timeline
Week 1: wound heals over with new skin. Week 2-3: scale pocket develops. Week 4-6: new scale emerges, initially thin and pale.
Week 7-12: scale thickens and pigments. Full color recovery can take 6 months in older arowana.
Color Issues
New scales often come in darker or paler than surrounding scales. This equalizes over 6-12 months with good diet and lighting.
For show arowana, even one mismatched scale reduces value. Keep pristine conditions to avoid loss in the first place.